amgbackend.hh

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#ifndef DUMUX_PARALLEL_AMGBACKEND_HH
#define DUMUX_PARALLEL_AMGBACKEND_HH
 
#include <memory>
 
#include <dune/common/exceptions.hh>
#include <dune/common/parallel/indexset.hh>
#include <dune/common/parallel/mpicommunication.hh>
#include <dune/common/parallel/mpihelper.hh>
#include <dune/grid/common/capabilities.hh>
#include <dune/istl/paamg/amg.hh>
#include <dune/istl/paamg/pinfo.hh>
#include <dune/istl/solvers.hh>
 
#include <dumux/linear/solver.hh>
#include <dumux/linear/parallelhelpers.hh>
 
namespace Dumux {
 
template <class LinearSolverTraits>
class AMGBiCGSTABBackend : public LinearSolver
{
public:
    AMGBiCGSTABBackend(const std::string& paramGroup = "")
    : LinearSolver(paramGroup)
    , isParallel_(Dune::MPIHelper::getCollectiveCommunication().size() > 1)
    {
        if (isParallel_)
            DUNE_THROW(Dune::InvalidStateException, "Using sequential constructor for parallel run. Use signature with gridView and dofMapper!");
 
        checkAvailabilityOfDirectSolver_();
    }
 
    AMGBiCGSTABBackend(const typename LinearSolverTraits::GridView& gridView,
                       const typename LinearSolverTraits::DofMapper& dofMapper,
                       const std::string& paramGroup = "")
    : LinearSolver(paramGroup)
#if HAVE_MPI
    , isParallel_(Dune::MPIHelper::getCollectiveCommunication().size() > 1)
#endif
    {
#if HAVE_MPI
        if (isParallel_)
            phelper_ = std::make_unique<ParallelISTLHelper<LinearSolverTraits>>(gridView, dofMapper);
#endif
        checkAvailabilityOfDirectSolver_();
    }
 
    template<class Matrix, class Vector>
    bool solve(Matrix& A, Vector& x, Vector& b)
    {
#if HAVE_MPI
        solveSequentialOrParallel_(A, x, b);
#else
        solveSequential_(A, x, b);
#endif
        return result_.converged;
    }
 
    std::string name() const
    {
        return "AMG-preconditioned BiCGSTAB solver";
    }
 
    const Dune::InverseOperatorResult& result() const
    {
        return result_;
    }
 
private:
    void checkAvailabilityOfDirectSolver_()
    {
#if !HAVE_SUPERLU && !HAVE_UMFPACK
        std::cout << "\nAMGBiCGSTABBackend: No direct solver backend found. Using iterative solver as coarse grid solver.\n"
                  << "Note that dune-istl currently hard-codes a tolerance of 1e-2 for the iterative coarse grid solver.\n"
                  << "This may result in reduced accuracy or performance depending on your setup.\nConsider installing "
                  << "UMFPack (SuiteSparse) or SuperLU or apply the istl patch, see dumux/patches/README.md." << std::endl;
#endif
    }
 
#if HAVE_MPI
    template<class Matrix, class Vector>
    void solveSequentialOrParallel_(Matrix& A, Vector& x, Vector& b)
    {
        if constexpr (LinearSolverTraits::canCommunicate)
        {
            if (isParallel_)
            {
                if (LinearSolverTraits::isNonOverlapping(phelper_->gridView()))
                {
                    using PTraits = typename LinearSolverTraits::template ParallelNonoverlapping<Matrix, Vector>;
                    solveParallel_<PTraits>(A, x, b);
                }
                else
                {
                    using PTraits = typename LinearSolverTraits::template ParallelOverlapping<Matrix, Vector>;
                    solveParallel_<PTraits>(A, x, b);
                }
            }
            else
                solveSequential_(A, x, b);
        }
        else
        {
            solveSequential_(A, x, b);
        }
    }
 
    template<class ParallelTraits, class Matrix, class Vector>
    void solveParallel_(Matrix& A, Vector& x, Vector& b)
    {
        using Comm = typename ParallelTraits::Comm;
        using LinearOperator = typename ParallelTraits::LinearOperator;
        using ScalarProduct = typename ParallelTraits::ScalarProduct;
 
        std::shared_ptr<Comm> comm;
        std::shared_ptr<LinearOperator> linearOperator;
        std::shared_ptr<ScalarProduct> scalarProduct;
        prepareLinearAlgebraParallel<LinearSolverTraits, ParallelTraits>(A, b, comm, linearOperator, scalarProduct, *phelper_);
 
        using SeqSmoother = Dune::SeqSSOR<Matrix, Vector, Vector>;
        using Smoother = typename ParallelTraits::template Preconditioner<SeqSmoother>;
        solveWithAmg_<Smoother>(A, x, b, linearOperator, comm, scalarProduct);
    }
#endif // HAVE_MPI
 
    template<class Matrix, class Vector>
    void solveSequential_(Matrix& A, Vector& x, Vector& b)
    {
        using Comm = Dune::Amg::SequentialInformation;
        using Traits = typename LinearSolverTraits::template Sequential<Matrix, Vector>;
        using LinearOperator = typename Traits::LinearOperator;
        using ScalarProduct = typename Traits::ScalarProduct;
 
        auto comm = std::make_shared<Comm>();
        auto linearOperator = std::make_shared<LinearOperator>(A);
        auto scalarProduct = std::make_shared<ScalarProduct>();
 
        using Smoother = Dune::SeqSSOR<Matrix, Vector, Vector>;
        solveWithAmg_<Smoother>(A, x, b, linearOperator, comm, scalarProduct);
    }
 
    template<class Smoother, class Matrix, class Vector, class LinearOperator, class Comm, class ScalarProduct>
    void solveWithAmg_(Matrix& A, Vector& x, Vector& b,
                       std::shared_ptr<LinearOperator>& linearOperator,
                       std::shared_ptr<Comm>& comm,
                       std::shared_ptr<ScalarProduct>& scalarProduct)
    {
        using SmootherArgs = typename Dune::Amg::SmootherTraits<Smoother>::Arguments;
        using Criterion = Dune::Amg::CoarsenCriterion<Dune::Amg::SymmetricCriterion<Matrix, Dune::Amg::FirstDiagonal>>;
 
        Dune::Amg::Parameters params(15, 2000, 1.2, 1.6, Dune::Amg::atOnceAccu);
        params.setDefaultValuesIsotropic(LinearSolverTraits::GridView::dimension);
        params.setDebugLevel(this->verbosity());
        Criterion criterion(params);
        SmootherArgs smootherArgs;
        smootherArgs.iterations = 1;
        smootherArgs.relaxationFactor = 1;
 
        using Amg = Dune::Amg::AMG<LinearOperator, Vector, Smoother, Comm>;
        auto amg = std::make_shared<Amg>(*linearOperator, criterion, smootherArgs, *comm);
 
        Dune::BiCGSTABSolver<Vector> solver(*linearOperator, *scalarProduct, *amg, this->residReduction(), this->maxIter(),
                                            comm->communicator().rank() == 0 ? this->verbosity() : 0);
 
        solver.apply(x, b, result_);
    }
 
#if HAVE_MPI
    std::unique_ptr<ParallelISTLHelper<LinearSolverTraits>> phelper_;
#endif
    Dune::InverseOperatorResult result_;
    bool isParallel_ = false;
};
 
} // end namespace Dumux
 
#endif